(1) Field of the Invention
This invention relates to split nuts used in blowout preventers temporarily installed on oil and gas wells. Applicant designates one with ordinary skill in the art as a mechanical engineer, or person having similar experience and training, engaged in the manufacture or repair of blowout preventers.
The blowout preventer art is a specialized area of the oil and gas well drilling and reworking fields. Problems are experienced in the design and construction of blowout preventers that are not encountered in other areas. Therefore, those with ordinary skill tend to restrict their search for solutions to the teachings of the existing blowout preventer art. Thus, applicant asserts that the pertinent art is limited to references relating to blowout preventers.
(2) Description of the Prior Art
During drilling, reworking or reentry operations, the well bore and well head may be highly pressurized, either by penetrating a pressurized reservoir or by intentionally applied mechanical forces. To contain these pressures reliably, blowout preventers are installed to block the well bore when necessary.
There are different types and designs of blowout preventers. Several designs incorporate "split nuts", or "brass nuts", and are the only blowout preventers that concern this invention. The remaining blowout preventers do not use split nuts of the type that my invention improves.
Blowout preventers that include split nuts typically include carriages that have sealing surfaces that mate with a round tube or drill string within the blowout preventer bore, or that include a "blind", to seal the blowout preventer bore. The split nuts are attached to the carriages. Actuating screws, journaled within the blowout preventer, are rotated to thread the split nuts, and hence the carriages along the screws to slide the carriages together.
The blowout preventers with split nuts are sometimes used with drilling operations, but are temporarily installed on wells during reworking or reentry operations. During such operations the entire system, or part thereof, may be intentionally pressurized, and acid, mud, cement, salt water, sand, or other media may be introduced through a tube within the preventer bore, or through a side port that is normally plugged when a "blind" is used to completely block or seal the bore, during acidizing, fracturizing, and recirculation operations.
The split nuts described thus far, used extensively and well known by workers in the well treatment arts, have been formed of brass, and are split into a cap and a base fastened together to form a threaded nut bore. Prior art split nuts, were made of brass and are also commonly referred to as "brass nuts", "brass", or "split nuts".
One problem experienced in the prior art is that the base and cap of the brass nuts were fastened together by steel bolts threaded into threaded holes in the brass base. For various reasons, such as the effects of corrosive materials used with blowout preventers, overtightening during assembly, wear and tear due to repeated disassembly and assembly encountered in cleaning and redressing the carriage sealing surfaces, or failure during use, the brass threads in the base into which the fastening bolts are tightened are stripped out. Of course, the brass or split nut can fail in other ways, such as splitting or cracking of the base, or simply wearing out the threads in the split nut bore. As between failure of the split nut and damage of the carriage or actuating screw, failure of the split nut is preferred. Therefore, the split nut is designed to fail before the carriage or actuating screws, so that the split nut acts as a "fuze".
Prior to my invention, brass nuts with stripped or damaged threads for fastening bolts, as well as those failed in other ways, were usually discarded and replaced with a new brass nut. Another problem encountered while using blowout preventers was corrosion of the fastening bolt threads and the bolt holes in the bore as corrosive materials seeped down the bolts past the holes in the cap.
Prior to filing this application, a search was made in the United States Patent and Trademark Office. That search developed the following United States Patents:
KOHN, U.S. Pat. No. 296,336; MATTHEWS, U.S. Pat. No. 354,331; TAYLOR, U.S. Pat. No. 2,291,846; BELKNAP, U.S. Pat. No. 3,731,504.
The patents developed during the search do not appear to applicant to be particularly pertinent to the limited subject matter of this application. However, applicant has provided citations thereof in the event that, as the product of the efforts of an experienced searcher, the Examiner might find them of interest.